Silicate weathering machine at work: Rock magnetic data from the late Paleocene-early Eocene Cicogna section, Italy

Abstract

We describe a scenario of climate forcing on sedimentation recorded in the late Paleocene-early Eocene Cicogna marine section from the Belluno Basin (NE Italy). Previously published magneto-biostratigraphic data revealed that the ∼81 m Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil zones (∼52.2-56.6 Ma). Using previously published rock magnetic data, augmented by data from this study, we describe and thoroughly discuss a pronounced increase of hematite (relative to maghemite or magnetite) between ∼54.9 and 54.6 Ma immediately above the Paleocene-Eocene boundary, followed by a second, long-term increasing trend from ∼54 Ma up to ∼52.2 Ma in the early Eocene. This hematite is essentially of detrital origin, insofar as it is associated with a strong shallow bias of paleomagnetic inclinations, and is interpreted to have formed on land by the weathering of Fe-bearing silicates and other primary minerals. We speculate that the warm and humid climate typical of the Paleocene-Eocene thermal maximum (PETM, ∼54.9 Ma) as well as of the warming trend leading to the early Eocene climatic optimum (EECO; ∼52-50 Ma) enhanced continental weathering of silicate rocks with the consequent production, transport, and sedimentation of detrital hematite grains. This hypothesis is confirmed by a statistical correlation between the rock magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature. Our temporal coupling between oxidation state of sedimentary magnetic phases and global climate is therefore consistent with the existence in the Paleocene-Eocene of the silicate weathering negative feedback mechanism for the long-term stabilization of the Earth's surface temperature. Copyright 2010 by the American Geophysical Union.